There are many situations where electromagnetic energy is required to be distributed into a rectangular output. In the vast majority of these situations a high efficiency transfer of source energy is desirable. This is particularly true in regulated lighting. For example, overland vehicle safety lighting, aircraft lighting, street lamp lighting and marine lighting often require specific output patterns that are mandated by government regulations to have minimum and maximum illumination values and which vary substantially in different directions. In each case, regulations typically have minimum photometric or radiometric requirements that must be met by the device. In many cases, the output distribution requirement is rectangular in angle space. Rectangular or rectangular shaped output distribution, refers to an output light distribution of some degrees in width as measured using a type A goniometer from a first plane and an output light distribution of a different number of degrees in width as measured using a type A goniometer along a second orthogonal plane. The resulting pattern is rectangular when plotted graphically on a Cartesian graph having a horizontal and vertical axis corresponding to the two axes of the type A goniometer.
References to electromagnetic radiation or light in this application are intended as references to the entire electromagnetic spectrum, including the visible spectrum and all non-visible wavelengths including but not limited to infrared, ultraviolet, x-ray, gamma ray and microwave wavelengths.
The present invention deals in particular with high aspect ratio rectangles where the rectangle is dimensionally wide in a first direction and narrow in a second orthogonal direction. For instance, an amber PC rated side-marker clearance light requires an even minimum intensity of 0.62 Candellas (Cd's) over 180 degrees in the horizontal plane and over 20 degrees in an orthogonal vertical plane as measured by a type A goniometer. In this instance, the 180 degrees by 20 degrees represents a high aspect ratio rectangle in angle space. This general type of pattern having a large major axis greater than 100 degrees in total width and having a minor axis less than 50 degrees in total width will be referred to as a High Aspect Ratio (HAR) rectangular output throughout this application.
Light Emitting Diodes or LED's are solid state electrical devices with high efficiencies and long lives. LED's are naturally impact resistant, use very little power and often have 100,000 hour life spans. These features make these devices preferable for use in safety lighting. The primary disadvantage of LED light sources is their cost. If the efficiency of an optical device to distribute light from the LED source into the regulated pattern could be improved, fewer LED's could be used resulting in a lower cost safety device.
In the past, high output LED's were typically manufactured with lenses incorporated over the emitting solid state chip or dice in a through-hole type electrical package The lens was typically employed to concentrate the LED light from the dice into a narrower high intensity pattern. Unfortunately, the nature of these lenses typically meant that complex secondary optics were required for use with the LED for redistributing the light into certain wide output regulated safety patterns. This increased the amount of LED source energy necessary to meet these HAR output pattern requirements.
Recently, LED manufacturers have turned to surface mountable LED devices that have superior heat removal from the diode junction and higher optical flux per watt. These devices are now being regularly provided with a flat output surface free from the source distorting optics of past LED's. These devices have very wide uncollimated output distributions with typical viewing angles greater than 100 degrees. The viewing angle for the purposes of this application is defined as the full angular width of the optical distribution where the light output reaches 50% of the intensity measured on the optical axis. LED's of this type have generally symmetrical outputs around the center or optical axis, thus a stated viewing angle of 10 degrees describes a conical output distribution where 50% of the peak intensity value occurs at 5 degrees from the optical or center axis of the device. A 120 degree viewing angle device, which is very common in wide output angle LEDs, defines a device which has an output intensity of 50% at an angle of 60 degrees from the optical axis.
High output LED's with hemispherical and output intensity closely following that of a Lambertian plane emitter have recently become increasingly available. These LED's output a highly diffuse illumination pattern with a very predictable intensity distribution closely following the trigonometric cosine function. However an unmodified hemispherical emitter is highly inefficient in meeting HAR rectangular output distribution as defined above.
LED devices with lenses incorporated therein have typically limited many of the devices to a narrow output pattern. The generation of high aspect ratio rectangles with widths greater than 90 degrees require the use of sensitive and delicate high angle reflective optical surfaces for the distribution of light beyond 45 degrees to the normal. The result is that many of these lights today incorporate multiple LED's arranged at different angles for generating the high angles required for the patterns.
One such design in production today uses a combination of axially revolved refractive and reflective surfaces from multiple old style LED's to collect and distribute the light into a +/−45 degree pattern. In this design, the axis of revolution of the inner surfaces is placed near the LED and run perpendicular to the long axis of the angle space rectangle defined by the requirement. The outer surfaces of the device made in accordance with this design typically consist of a single or just a few planes and did not consist of complex shapes. This type of optical lens has been in production since at least 1999. Unfortunately, the narrow output of the older LED sources and simple planar outer surfaces make this type of optic impractical for meeting evenly illuminating wider rectangular requirements.